Nowadays, LED lighting devices are increasingly used in motor vehicles, by means of which suitable light distributions are generated for signal lights or headlights of the vehicle.
LEDs are used in motor vehicles also in combination with optical waveguides, into which the light of the LEDs is coupled and is guided through the optical waveguide. A coupling-out surface is formed in the longitudinal direction of the optical waveguide, which coupling-out surface deflects light in the optical waveguide, so that the light exits by way of an exit surface of the optical waveguide. German Patent document DE 103 17 062 A1 shows an LED lighting device having an optical waveguide, in which lighting device the coupling-out surface coincides with the light exit surface. A light distribution can be generated by use of this lighting device, which extends in the longitudinal direction of the optical waveguide. Because of the low luminance of the LEDs used for generating light, however, only optical waveguides of a limited length and/or of a minimal cross-sectional surface can be used.
It is an object of the invention to create a lighting device for a motor vehicle by which a light distribution can be efficiently generated by using an optical waveguide.
This and other objects are achieved by a lighting device, according to the invention, for a motor vehicle, particularly for a passenger car and optionally also for a commercial vehicle. The device includes an optical waveguide for the totally reflective guiding of light along a light propagation direction, in which case the light originates from at least one light source which is a component of the lighting device. In this case, the light is coupled in by way of at least one coupling-in surface at a face of the optical waveguide, in which case the optical waveguide further includes a coupling-out surface arranged along the light propagation direction for the coupling-out of light from the optical waveguide, so that the decoupled light exits from the optical waveguide on an exit surface arranged along the light propagation direction while the total reflection condition is eliminated. The coupling-out surface and the exit surface therefore also have a dimension transversely to the light propagation direction. The optical waveguide is preferably further developed to be oblong and optionally rod-shaped, in this case, the longitudinal direction of the optical waveguide corresponding to the light propagation direction. The lighting device according to the invention is distinguished by the fact that at least one light source, whose light can be coupled in by way of the at least one coupling-in surface, is a laser light source. This laser light source preferably generates monochromatic light.
The use of a laser light source in combination with optical waveguides has the important advantage that, because of the high luminance of the laser light source, the light can be coupled out with sufficient intensity over long distances in the optical wave guide. Furthermore, optical waveguides with a small cross-section can be installed in the lighting device.
The optical waveguide of the lighting device according to the invention may be constructed in different fashions. In particular, the optical waveguide may be further developed precisely as in the lighting device of German Patent document DE 103 17 062 A1. The entire disclosure of DE 103 17 062 A1 is hereby expressly incorporated by reference as non-essential matter.
In a particularly preferred embodiment, the laser light source of the lighting device is a punctiform light source, and/or a converter device is provided for converting the light of the laser light source to a punctiform light source. The converter device comprises particularly a front lens system and/or a phosphor conversion layer which generates, from monochromatic laser light, a punctiform white light source or a punctiform light source with a wavelength different from that of the laser light. Phosphor conversion layers per se are known from the prior art. For example, in the case of a blue laser light source with an emission wavelength of 450 nm, a phosphor conversion layer of Ce:YAG phosphor can be used for generating white light. For violet laser light with a wavelength of 405 nm, particularly a phosphor conversion layer of cerium-doped nitride phosphor or cerium-doped oxynitride phosphor is used.
Within the meaning of the invention, a “punctiform light source” is a light source having a very small radiating surface which, with respect to the dimensions of the lighting device in a very good approximation can be assumed to be punctiform such that all rays of the light source originate from a single point. The maximal dimension of the punctiform light source in the top view, i.e. in the main radiation direction with the greatest intensity of the light source, in a particularly preferred embodiment, amounts to 500 μm or less, preferably 100 μm or less, and particularly preferably 20 μm or less. Furthermore, in the top view, the punctiform light source preferably has an emitting surface of 0.5 mm2 or less, particularly of 0.01 mm2 or less, and particularly preferably of 0.0002 mm2 or less. The punctiform light source includes particularly an emitting cornered surface whose edges each have a length of 500 μm or less and preferably 20 μm or less. Nevertheless, the punctiform light source may also have a round emitting surface. The punctiform light source with the above-described dimensions is preferably further developed such that it generates a light flux of 100 lm or more and particularly of 200 lm or more and/or has a radiant power of 1 watt or more and/or a luminance of at least 108 Cd/m2 and particularly of 109 Cd/m2 or more. Such punctiform light sources can only be obtained by laser light, for example, by using laser diodes.
In a particularly preferred embodiment, the light of the laser light source and, particularly of the punctiform light source, is converted at the at least one coupling-in surface of the optical waveguide by way of a collimator to a collimated luminous beam. In this case, the collimator may be formed by a curved face, on which the light of the punctiform laser light source is diffracted or reflected. The curved face may form a transmitting lens on which the light of a laser light source provided outside the optical waveguide is incident. Likewise, as required, there is the possibility that the laser light source is arranged in the optical waveguide, for example, in a recess at the coupling-in surface and radiates in the direction of the boundary surface formed by the coupling-in surface between the optical waveguide and the surrounding medium, the light being reflected at this boundary surface and guided back into the optical waveguide as a collimated luminous beam.
In a further embodiment, the lighting device according to the invention is further developed such that, by way of a front lens system, a collimated laser beam is generated from the light of the laser light source. In this case, the laser light source and the front lens system may optionally form a unit for generating the laser beam, which conventionally is also called a laser. The collimated laser beam is coupled by way of the preferably plane coupling-in surface into the optical waveguide, in which case the laser beam is preferably guided to the coupling-in surface by way of a beam deflection. In a very flexible manner, the light of a laser light source can thereby be coupled from different initial positions into the optical waveguide. The installation space in the vehicle can therefore be efficiently utilized. Furthermore, by way of the laser light, a ray beam is generated which has a high luminance and which can also be coupled into optical waveguides of compact dimensions and particularly with a small cross-section and can be guided there over long distances.
In a further, particularly preferred embodiment, the laser light source and, particularly the punctiform light source, is a laser diode. The laser light source preferably is a monochromatic light source whose light is converted by a phosphor conversion layer to white light or to light of a different wavelength than the light of the monochromatic light source, in which case the phosphor conversion layer is particularly arranged in front of the face of the optical waveguide, is mounted in a recess of the optical waveguide, and/or is formed on the coupling-out surface of the optical waveguide. The phosphor conversion layer may optionally also form the coupling-out surface and/or be mounted following the coupling-out surface outside the optical waveguide.
In a further, particularly preferred embodiment, the coupling-out surface has a deflecting device and particularly a prism arrangement or a roughened surface, by way of which light impinging on the coupling-out surface is deflected in the optical waveguide to the exit surface. In this case, the roughened surface may be further developed analogous to that in the optical waveguide of German Patent document DE 103 17 062 A1.
In a particularly preferred embodiment, the deflecting device is further developed such that the intensity of the light exiting by way of the exit surface remains essentially constant along the light propagation direction or longitudinal direction of the optical waveguide, which can be achieved, for example, by a continuous widening of the dimension of the prism arrangement or the roughened surface transversely to the light propagation direction while the distance from the coupling-in surface is increased.
In a further preferred embodiment of the lighting device according to the invention, the exit surface of the optical waveguide is curved in such a manner that collimated light exits from the exit surface. However, an (additional) deflection arrangement, particularly in the form of a reflector and/or of a lens, may be provided, which generates collimated light from the light exiting from the exit surface. In particular, the deflection arrangement described in German Patent document DE 103 17 062 A1 can be used for this purpose.
Depending on the further development, the lighting device may have an optical waveguide with a rectangular or round cross-section. In this case, the maximal dimension of the cross-section preferably is 10 mm or less. However, the optical waveguide may also be further developed such that one edge in the rectangular cross-section of the optical waveguide has a length of 10 mm or more, whereas the other edge has a length of 4 mm or less, so that a laminar optical waveguide is formed. The light exiting takes place particularly essentially perpendicular to the longer edge and essentially parallel to the shorter edge. Particularly, flat optical waveguides can therefore be used in the lighting device according to the invention.
The lighting device according to the invention can be provided for generating arbitrary light distributions. The lighting device is preferably used as a signal light, such as a daytime running light, a marker light, a turn signal light, an indicator light, a tail light and/or a brake light. The lighting device may, however, optionally also form a headlight for the active illumination of the environment of the vehicle, such as a low-beam light or a high-beam light.
In a further variant of the lighting device according to the invention, the coupling-out surface and the exit surface are identical, which is also the case in the lighting device of German Patent document DE 103 17 062 A1.
In addition to the above-described lighting device, the invention further relates to a motor vehicle which includes one or more lighting devices according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.